1. Field of the Invention
The invention relates to a device to be used for a liquid crystal display (LCD), and more particularly to such a device capable of color-display.
2. Description of the Related Art
A part of a conventional device to be used for a liquid crystal display is illustrated in FIGS. 1A to 1C; FIG. 1A is a plan view of a device, FIG. 1B is a cross-sectional view taken along the line I--I in FIG. 1A, and FIG. 1C is a cross-sectional view taken along the line II--II in FIG. 1A.
With reference to FIG. 1C, a pair of substrates 1 and 2 are first adhesively connected to each other at margins thereof through sealing material 3 such as an adhesive so that the substrates 1 and 2 are spaced away from each other in parallel with each other. The thus connected substrates 1 and 2 are baked, and then liquid crystal 4 is filled in a space formed between the substrates 1 and 2, thereby a device to be used for a liquid crystal display being completed. In practice, in order to obtain a controlled width of the liquid crystal layer, a filler is contained in both the sealing material 3 and the liquid crystal layer.
On inner surfaces of the substrates 1 and 2 are formed various layers. On an inner surface of the substrate 1 are formed a display pixel electrode array 5 to be driven by a thin film transistor, and an orientation film 6 over the electrode array 5. The orientation film 6 is a film having been rubbed in order to control molecular orientation of the liquid crystal 4. In a margin of the substrate 1 are disposed terminal electrodes 7 drawn out beyond the sealing material 3 for use of driving modules.
On an inner surface of the substrate 2 disposed in facing relation to the substrate 1 are formed color filter layers 8 in alignment with the electrode array 5. The color filter layers 8 include three layers for red (R), green (G) and blue (B) (only R is illustrated in FIG. 1C). Among the color filter layers are formed black matrices or light-impermeable patterns 9. The black matrix disposed at the margin extends between the color filter layer and the sealing material 3. The color filter layers 8 and the black matrices 9 are covered with an overcoat layer 10 in order to prevent ingredients of the color filter layers 8 from penetrating the liquid crystal 4, and enhance flatness of surfaces of the color filter layers 8.
Over the overcoat layer 10 is formed a common electrode 11. Similarly to the substrate 1, the substrate 2 includes the orientation film 6 formed over the common electrode 11.
Various attempts have been made in prior art to increase adhesive strength between the substrates 1 and 2 through the sealing material 3.
For instance, Japanese Unexamined Patent Publication No. 57-99614 has suggested using electrodes made of glass because adhesive strength between the sealing material and glass is greater than adhesive strength between the sealing material and polyimide or ITO (Indium-Tin-Oxide).
For another instance, Japanese Unexamined Patent Publication No. 4-141623 has suggested a liquid crystal panel including a pair of substrates. Color filter layers are formed on one of the substrates, and there is also formed an overcoat layer which covers at least a surface of the color filter layers except portions at which sealing material is to be adhered. Namely, the overcoat layer is not formed beneath a region at which the sealing material is to be adhered.
Japanese Unexamined Patent Publication No. 5-265009 has proposed a device to be used for a liquid crystal display in which an overcoat layer is patterned, and with no overcoat layer or ITO located beneath the region at which the sealing material is to be adhered, thereby increasing adhesive strength between substrates facing each other and an adhesive layer.
Japanese Unexamined Patent Publication No. 2-87116 has suggested a color filter substrate to be used for a liquid crystal display in which transparent electrodes are partially cut out at portions through which transparent electrodes and sealing material are adhesively connected to each other, thereby increasing accuracy of surfaces of the substrates and the sealing material through which they are adhered to each other, sealing performance, and adhesive strength.
As best shown in FIG. 1C, the sealing material composed of epoxy resin, for instance, is usually in partial contact with black matrix (usually composed of chromium) formed on a color filter substrate. In general, the adhesive force between epoxy resin and chromium is weaker than the adhesive force between epoxy resin and glass. Thus, long term use of a liquid crystal display weakens the adhesive force between epoxy resin and chromium with the result of less reliability.
In addition, if glass is used as underlying material beneath a region at which epoxy resin is to be adhered, incident light emitted from back light may escape outside through marginal sealing areas, which are composed of glass and hence transparent, with a resulting deterioration of display performance.